This invention relates in general to earth boring bits, and in particular to the bearings between the rotatable cutters and bearing pins.
A typical drill bit for drilling oil and gas wells has three rotatable cutters mounted on depending bearing pins. As the bit rotates, the cutters rotate on their respective bearing pins. Earth disintegrating teeth on the cutters disintegrate the earth formation to drill the well.
The bearings between the cutters and the bearing pin are subject to very large forces, resulting in heat generation and deterioration of the bearing. In general, there are two main types of bearings. One type of bearing uses a roller bearing, an example of which is shown in U.S. Pat. No. 3,720,274, Hugh F. McCallum, issued Mar. 13, 1973. The roller bearings are cylindrical bearings spaced between the cavity of the cutter and the bearing pin. The bit in that patent utilizes passages for circulating drilling fluid, normally air, between the roller bearings. Another type of roller bearing bit uses liquid lubricant such as grease in the roller bearing areas.
Another type of bit utilizes a friction or journal bearing, an example of which is shown in U.S. Pat. No. Re. 28,625, Robert A. Cunningham, reissued Nov. 25, 1975. In that type of bit, the cavity of the cutter mates in sliding and rotating contact with the bearing pin. In some embodiments, axially aligned grooves are placed in the bearing surfaces for containing a soft metal such as silver. Liquid lubricant such as grease is normally supplied from a reservoir that is sealed and pressure compensated to maintain the pressure in the bearing areas about the same as the exterior pressure.
For cooling, the journal bearing bit relies on drilling fluid circulated through nozzles to the exterior of the bit. While journal bearing bits are successful, increasing the life of the bearing by enhanced cooling is desirable.